Mixtures or blends of low-unsaturation rubbery polymers with highly unsaturated rubbery polymers are of practical importance because of the superior ozone resistance imparted to the blend of the low-unsaturation rubber. Unfortunately, the presence of the low-unsaturation rubber also affects the mechanical and hysteresis characteristics of the vulcanizates in an adverse manner, as manifested by lower tensile strength and modulus values, and by higher dynamic heat build-up and permanent set. These undesirable phenomena are generally the result of the mutual insolubilities of the two types of rubber, the substantially slower cure rate of the low-unsaturation rubber, and the greater affinity of the typically polar curatives for the high-unsaturation rubber. As a net result, the vulcanized blend is a heterogeneous dispersion of largely uncured low-unsaturation rubber in well cured high-unsaturation rubber. The degraded mechanical and hysteresis properties caused by this unbalanced cure severely limit, or preclude, the use of such blends in articles subjected to severe service requirements such as tires. A process for improving the physical and dynamic properties of such rubbery polymer vulcanized blends is of considerable commercial practical importance.
It is, therefore, an object of this invention to provide a modified rubbery polymer having a low degree of unsaturation, a process for its preparation and composites of blends of such modified rubbery polymer with high-unsaturation rubbery polymers.
U.S. Pat. No. 3,915,907 and U.S. Pat. No. 3,970,133 disclose a rubbery composition which is comprised of an admixture of a rubbery terpolymer of ethylene, .alpha.-olefin containing 3 to 6 carbon atoms and a non-conjugated diene containing 6 to 12 carbon atoms with an N-chlorothio-sulfonamide of the formula: ##STR1## wherein the mole ratio of said N-chlorothio-sulfonamide to unsaturated sites in said terpolymer is in the range of about 0.06/1 to about 1/1, where R.sup.1 and R.sup.2 are selected from the group consisting of alkyl radicals having 1 to 20 carbon atoms, aralkyl radicals having 7 to 20 carbon atoms, alkaryl radicals having from 7 to 20 carbon atoms, and haloaryl radicals having 6 to 10 carbon atoms and where R.sup.1 is also selected from radicals having the formula: ##STR2## where R.sup.3 and R.sup.4 are individually selected from said alkyl, aralkyl, and haloaryl radicals and where R.sup.3 and R.sup.4 can be joined together to represent radicals selected from --CH.sub.2 --.sub.n, where n is an integer of 4 to 7, and --(CH.sub.2).sub.2 --O--(CH.sub.2)--.sub.2.
U.S. Pat. No. 3,915,907 and U.S. Pat. No. 3,970,133 disclose several techniques which can be utilized to incorporate chlorothio-sulfonamides into rubbery terpolymers. One such method involves addition of the chlorothio-sulfonamide to a solution of the polymer in an inert organic solvent, such as heptane, hexane, tetrachloroethylene, cyclohexane, methyl cyclohexane, chloroform, benzene or toluene. More polar solvents are preferred since they increase the rate of formation of polymer bound adduct. For example, adduct formation occurs much more rapidly in chloroform as a solvent than in hexane. A mixture of nonpolar solvent with a highly polar solvent may be used advantageously. For example, a mixture of 40 volumes of hexane and 1 volume of acetic acid can produce substantially faster adduct formation as compared to hexane alone. Furthermore, the rate of adduct formation can apparently be markedly improved by contact or catalysis with anhydrous zinc chloride.
A second method comprises swelling a solution of the chlorothio-sulfonamide into the polymer using the same type of solvents. Preferably, the solvent/polymer ratio is selected so that essentially all the solvent is taken up by the polymer. For this process, it is preferable that the polymer is first prepared in the form of small chunks, or crumbs, and the solvent then added.
A third technique comprises directly milling the chlorothio-sulfonamide into the polymer by means of an internal mixer (Banbury or extruder type) or an open roll mill. For direct mixing, it is advantageous to suspend or dissolve the chlorothio-sulfonamide in a relatively inert medium such as mineral oil or chlorinated paraffin in order to improve dispersion as well as minimize hydrolysis by atmospheric moisture.
In practice it has proven to be difficult to modify rubbery elastomers with N-chlorothio-sulfonamides due to slow reaction rates. For this reason, techniques for accelerating the reaction of N-chlorothio-sulfonamides and rubbery terpolymers, such as EPDM rubbers, have been sought.